Referring to FIG. 9, a NC machine tool disclosed in JP-B 6-75814 for machining a workpiece W to shape a noncircular part, having an elliptic or noncircular cross section, of a piston holds the workpiece W on the spindle that rotates about an axis C, rotates the spindle, minutely controls the movement, for radial feed in directions along the Y-axis, of a tool H held on a tool holder of the NC machine tool in synchronism with the rotation of the spindle and moves the tool H for longitudinal feed in directions along the Z-axis.
The surface shape of the noncircular part of the piston is specified by matrix data designating the position of a point by a distance from the origin on the axis C of the spindle, namely, the Z axis, an angle about the axis C, and a radial distance on the Y-axis.
As shown in FIG. 9, a piston formed by machining the workpiece W has a land part A provided with ring grooves for receiving piston rings and a skirt part B continuous with the land A. A noncircular part having a noncircular cross section is included, in most cases, in the skirt part B. The edge of the skirt part B in directions along the Z axis, namely, the profile, is irregular. A NC machining data generator for generating machining data for controlling NC machining for forming such a surface shape is proposed in JP-A 7-319528.
The machining data generator mentioned in JP-A 7-319528 generates axial shape data and radial shape data by from numerical data specifying a polygon, and generates NC machining data by combining the axial shape data and the radial shape data. Shape data for controlling machining to form the noncircular part is given directly to the NC machining data generator by a keyboard, and data specifying machining conditions including the rotating speed of the workpiece about the axis C and longitudinal feed along the Z-axis for forming the noncircular part is given directly to the NC machining data generator by a keyboard.
The shape data and the machining data on machining conditions need to be given separately to the prior art machining data generator mentioned in JP-A 7-319528. Therefore, those data must be individually managed and require troublesome management work.
As mentioned above, the piston has the cylindrical land part A having the circular part with a circular cross section, and the skirt part B having the noncircular part with a noncircular cross section. An actual turning operation forms the land part A continuously with the skirt part B. Shape data needed for machining the land part A is given separately to the prior art machining data generator. Thus, those data are given separately by separate data input operations. When the data input operations are performed separately, errors are liable to be made in entering data, and entering or loading the same data again into the machining data generator is a very time-consuming job.
It is an object of the present invention to provide a machining data generator for generating machining data for shaping a piston by NC machining, capable of previously collecting shape data on a noncircular part of the piston, namely, matrix data, and other condition data necessary for forming the general external shape of the piston, such as machining condition data and additional shape data on parts other than the noncircular part, in a single machining data sheet, to save individually managing various data and to enter the relevant data collectively.
Another object of the present invention is to provide a machining data generator for generating machining data for shaping a piston by NC machining, capable of easily examining the appropriateness of shape data on a noncircular part of the piston and of intuitively correcting shape data on the noncircular part.
A third object of the present invention is to provide a machining data generator for generating machining data for shaping a piston by NC machining, capable of easily examining the appropriateness of generated NC machining data.